That's a great question! I've just filmed a video to answer it, but it will be a couple of days before it's up.
In the mean time,
The stitches you're supposed to knit look like V's. The stitches you're supposed to purl look like dashes. You can watch the video on doing ribbing (Basic Techniques/More page), which talks about how to recognize a purl and knit stitch.
KnittingHelp Queen Bee
It is not because things are so difficult that we do not dare; it is because we do not dare that they are difficult.